1. Field of the Invention
The present invention relates generally to surface-coated machining tools, and more specifically to surface-coated machining tools employed in routing, slitting, drilling, and like processes on printed circuit boards onto which integrated circuits and various electronic parts are populated.
2. Description of the Background Art
In processing the peripheral form of circuit boards, press-working has been largely employed to date. Because printed circuit boards are structured by sandwiching copper foil into epoxy resin incorporating glass fiber, however, particulate matter produced when press-working has been a problem in the working environment. Therein, a machining tool referred to as a “router cutter,” with which slitting and routing processes are carried out on printed circuit boards, is used. An advantage to a milling machine employing the router cutter is that since the work is carried out while the cut end is under suction, there is no risk that chips will scatter externally.
Meanwhile, the tasks of miniaturizing electronic devices and making them lightweight have become a must in recent years, and owing to demands for heightening the density and precision in how components populate printed circuit boards—which are pivotal to actual operation—the dimension of the slots formed by routing is being made smaller and smaller, and correspondingly the diameter of the router cutter has come to be 3.175 mm or less.
Likewise, with the number of boards in a printed-circuit-board stack processed at once having increased and the processing speed gone up in order to improve working performance and reduce manufacturing costs, a consequent problem has been that router cutters have turned out to be inadequate in strength, breaking during jobs and producing burrs on printed circuit boards, rendering them unusable.
The router cutter presented in Japanese Pat. No. 3065547, for example, addresses this situation by furnishing a reinforcing rib on the chisel-face side of the router-cutter bit, enhancing the rigidity of the bit and improving the router cutter strength that had been a problem conventionally, to serve as a remedy against breakage accidents during machining jobs.
Meanwhile, in forming small-diameter holes in printed circuit boards given advances in heightening the density of and in laminating the printed circuit boards, machining tools referred to as miniature-drills are being widely used for PCB (printed circuit board) processing. Likewise, owing to calls for heightened density and precision in how components populate printed circuit boards, the holes formed in them by PCB-processing miniature-drills have become more and more micro-dimensioned, in accordance with which the diameter of the PCB-processing miniature-drills has come to be 0.3 mm or less. In order to improve working efficiency and reduce manufacturing costs, furthermore, processing speeds have accelerated; and given the circumstances, a consequent problem has been that PCB-processing miniature-drills have turned out to be inadequate in strength, breaking during jobs and producing burrs on printed circuit boards, which has been a cause of defective products.
In Japanese Pub. Pat. App. No. 10-138027, for example, this situation is addressed by utilizing a cemented carbide as the material for the PCB-processing miniature-drill presented therein, and by coating the surface with a hard carbon film deposited employing a hydrocarbon gas (methane), to improve resistance to, and serve as a remedy against, breakage.
Nevertheless, with demands from users for heightening the component surface-mounting density and precision growing more and more intense, the diameter of the router cutter that performs routing and slitting processes has come to be 1.6 mm or less—half what had been conventional—and preventing breakage defects during processing has turned out to be difficult merely by the above-described improvement in tool form.
By the same token, accompanying the growing intensity in demands for heightening the component surface-mounting density and precision has been the utilization of PCB-processing miniature-drills 0.2 mm or less in diameter to perform the drilling processes; but drills that perform adequately have not been obtainable with the above-described hard carbon film deposited using a hydrocarbon gas, in that the film hardness is low because hydrogen gets mixed into the film.